Magnetic resonance imaging agents

ABSTRACT

Novel magnetic resonance imaging agents comprise complexes of paramagnetic ions with aminoalkylamide derivatives of diethylenetriaminepentaacetic acid (&#34;DTPA&#34;) or ethylenediaminetetraacetic acid (&#34;EDTA&#34;) or other polyaminocarboxylic or cyclic polyaminocarboxylic chelating agents. These novel imaging agents are characterized by excellent NMR image-contrasting properties and by high solubilities in physiological solutions. 
     A novel method of performing an NMR diagnostic procedure involves administering to a warm-blooded animal an effective amount of a complex as described above and then exposing the warm-blooded animal to an NMR imaging procedure, thereby imaging at least a portion of the body of the warm-blooded animal.

This is a division of application Ser. No. 07/402,623, filed Sep. 5,1989, now U.S. Pat. No. 5,011,925 granted Apr. 22, 1991. ApplicationSer. No. 07/402,623 is a continuation-in-part of application Ser. No.321,265, filed Mar. 9, 1989, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to nuclear magnetic resonance (NMR) imaging and,more particularly, to methods and compositions for enhancing NMRimaging.

The recently developed technique of NMR imaging encompasses thedetection of certain atomic nuclei utilizing magnetic fields andradio-frequency radiation. It is similar in some respects to x-raycomputed tomography (CT) in providing a cross-sectional display of thebody organ anatomy with excellent resolution of soft tissue detail. Ascurrently used, the images produced constitute a map of the protondensity distribution and/or their relaxation times in organs andtissues. The technique of NMR imaging is advantageously non-invasive asit avoids the use of ionizing radiation.

While the phenomenon of NMR was discovered in 1945, it is onlyrelatively recently that it has found application as a means of mappingthe internal structure of the body as a result of the originalsuggestion of Lauterbur (Nature, 242, 190-191 (1973)). The fundamentallack of any known hazard associated with the level of the magnetic andradio-frequency fields that are employed renders it possible to makerepeated scans on vulnerable individuals. In additional to standard scanplanes (axial, coronal, and sagittal), oblique scan planes can also beselected.

In an NMR experiment, the nuclei under study in a sample (e.g. protons)are irradiated with the appropriate radio-frequency (RF) energy in ahighly uniform magnetic field. These nuclei, as they relax, subsequentlyemit RF at a sharp resonance frequency. The resonance frequency of thenuclei depends on the applied magnetic field.

According to known principles, nuclei with appropriate spin, when placedin an applied magnetic field (B, expressed generally in units of gaussor Tesla (10⁴ gauss)) align in the direction of the field. In the caseof protons, these nuclei precess at a frequency, f, of 42.6 MHz at afield strength of 1 Tesla. At this frequency, an RF pulse of radiationwill excite the nuclei and can be considered to tip the netmagnetization out of the field direction, the extent of this rotationbeing determined by the pulse duration and energy. After the RF pulse,the nuclei "relax" or return to equilibrium with the magnetic field,emitting radiation at the resonant frequency. The decay of the emittedradiation is characterized by two relaxation times, i.e., T₁, thespin-lattice relaxation time or longitudinal relaxation time, that is,the time taken by the nuclei to return to equilibrium along thedirection of the externally applied magnetic field, and T₂, thespin-spin relaxation time associated with the dephasing of the initiallycoherent precession of individual proton spins. These relaxation timeshave been established for various fluids, organs and tissues indifferent species of mammals.

In NMR imaging, scanning planes and slice thicknesses can be selected.This selection permits high quality transverse, coronal and sagittalimages to be obtained directly. The absence of any moving parts in NMRimaging equipment promotes a high reliability. It is believed that NMRimaging has a greater potential than CT for the selective examination oftissue characteristics in view of the fact that in CT, x-ray attenuationcoefficients alone determine image contrast, whereas at least fiveseparate variables (T₁, T₂, proton density, pulse sequence and flow) maycontribute to the NMR signal. For example, it has been shown (Damadian,Science, 171, 1151 (1971)) that the values of the T₁ and T₂ relaxationin tissues are generally longer by about a factor of 2 in excisedspecimens of neoplastic tissue compared with the host tissue.

By reason of its sensitivity to subtle physicochemical differencesbetween organs and/or tissues, it is believed that NMR may be capable ofdifferentiating different tissue types and in detecting diseases whichinduce physicochemical changes that may not be detected by x-ray or CTwhich are only sensitive to differences in the electron density oftissue.

As noted above, two of the principal imaging parameters are therelaxation times, T₁ and T₂. For protons (or other appropriate nuclei),these relaxation times are influenced by the environment of the nuclei(e.g., viscosity, temperature, and the like). These two relaxationphenomena are essentially mechanisms whereby the initially impartedradio frequency energy is dissipated to the surrounding environment. Therate of this energy loss or relaxation can be influenced by certainother nuclei which are paramagnetic. Chemical compounds incorporatingthese paramagnetic nuclei may substantially alter the T₁ and T₂ valuesfor nearby protons. The extent of the paramagnetic effect of a givenchemical compound is a function of the environment within which it findsitself.

In general, paramagnetic divalent or trivalent ions of elements with anatomic number of 21 to 29, 42 to 44 and 58 to 70 have been foundeffective as NMR image contrasting agents. Suitable such ions includechromium (III), manganese (II), manganese (III), iron (III), iron (II),cobalt (II), nickel (II), copper (II), praseodymium (III), neodymium(III), samarium (III) and ytterbium (III). Because of their very strongmagnetic moments, gadolinium (III), terbium (III), dysprosium (III),holmium (III) and erbium (III) are preferred. Gadolinium (III) ions havebeen particularly preferred as NMR image contrasting agents.

Typically, the divalent and trivalent paramagnetic ions have beenadministered in the form of complexes with organic complexing agents.Such complexes provide the paramagnetic ions in a soluble, non-toxicform, and facilitate their rapid clearance from the body following theimaging procedure. Gries et al., U.S. Pat. No. 4,647,447, disclosecomplexes of various paramagnetic ions with conventional aminocarboxylicacid complexing agents. A preferred complex disclosed by Gries et al. isthe complex of gadolinium (III) with diethylenetriaminepentaacetic acid("DTPA"). This complex may be represented by the formula: ##STR1##

Paramagnetic ions, such as gadolinium (III), have been found to formstrong complexes with DTPA. These complexes do not dissociatesubstantially in physiological aqueous fluids. The complexes have a netcharge of -2, and generally are administered as soluble salts. Typicalsuch salts are the sodium and N-methylglucamine salts.

The administration of ionizable salts is attended by certaindisadvantages. These salts can raise the in vivo ion concentration andcause localized disturbances in osmolality, which in turn, can lead toedema and other undesirable reactions.

Efforts have been made to design non-ionic paramagnetic ion complexes.In general, this goal has been achieved by converting one or more of thefree carboxylic acid groups of the complexing agent to neutral,non-ionizable groups. For example, S. C. Quay, in U.S. Pat. Nos.4,687,658 and 4,687,659, discloses alkylester and alkylamidederivatives, respectively, of DTPA complexes. Similarly, published WestGerman applications P 33 24 235.6 and P 33 24 236.4 disclose mono- andpolyhydroxyalkylamide derivatives of DTPA and their use as complexingagents for paramagnetic ions. Published Australian Patent ApplicationNo. 78995/87 also describes amide complexing agents useful in NMR andx-ray procedures.

The nature of the derivative used to convert carboxylic acid groups tonon-ionic groups can have a significant impact on tissue specificity.Hydrophilic complexes tend to concentrate in the interstitial fluids,whereas lipophilic complexes tend to associate with cells. Thus,differences in hydrophilicity can lead to different applications of thecompounds. See, for example, Weinmann et al., AJR, 142, 679 (Mar. 1984)and Brasch et al., AJR, 142, 625 (Mar. 1984).

Thus, a need continues to exist for new and structurally diversenon-ionic complexes of paramagnetic ions for use as NMR imaging agents.

SUMMARY OF THE INVENTION

The present invention provides novel complexing agents and complexes ofcomplexing agents with paramagnetic ions. The complexes are representedby either of the following formulae: ##STR2## wherein A is --CHR² --CHR³-- or ##STR3## M^(+Z) is a paramagnetic ion of an element with an atomicnumber of 21-29, 42-44 or 58-70, and a valence, Z, of +2 or +3; R¹groups may be the same or different and are selected from the groupconsisting of --O⁻ and ##STR4## wherein R⁴, R⁵ and R⁶ may be the same ordifferent and are hydrogen, alkyl, hydroxy, alkoxy, mono- orpolyhydroxyalkyl, alkoxyalkyl, aminoalkyl or acylaminoalkyl wherein thecarbon-containing portions contain from 1 to about 6 carbon atoms or R⁵and R⁶, together with the adjacent nitrogen, can form a heterocyclicring of five, six or seven members wherein 0 to 1 members other than thenitrogen are ##STR5## and which members are unsubstituted or substitutedby hydroxy, alkyl, aryl, hydroxyalkyl, aminoalkyl, aminoaryl,alkylamino, or carbamoyl wherein the substituents contain from 1 toabout 6 carbon atoms,

n is between 1 and 6;

R² and R³ may be the same or different and are hydrogen, alkyl havingfrom 1 to about 6 carbon atoms, phenyl or benzyl or R² and R³ togetherwith the intervening carbon can form a hydrocarbon ring of 5, 6 or 7members;

and wherein Z of the R¹ groups are --O⁻ and the remainder of the R¹groups are ##STR6##

Alternatively, the complexes are represented by the following formula:II. ##STR7## wherein M^(+z) is a paramagnetic ion of an element with anatomic number of 21-29, 42-44 or 58-70, and a valence Z of +2 or +3,

r and s are integers between 1 and 6 and can be the same or different,

The R' groups can be the same or different and are selected from thegroup consisting of hydrogen, alkyl having from 1 to 6 carbon atoms andmono or polyhydroxyalkyl, the alkyl portion having from 1 to 6 carbonatoms,

the R^(1') groups can be the same or different and are selected from thegroup consisting of --O⁻ and ##STR8## wherein R^(2') is selected fromthe group consisting of (CH₂ CH₂ O)_(p) -- R^(3') and ##STR9## andR^(4') is selected from the group consisting of H, R^(2') and R^(3'),wherein R^(3'), R^(5') and R^(6') can be the same or different and areselected from the group consisting of hydrogen, alkyl, hydroxy, alkoxy,mono- or poly-hydroxyalkyl, alkoxyalkyl, aminoalkyl or acylamino-alkyl,wherein the carbon-containing portions contain from 1 to about 6 carbonatoms or R^(5') and R^(6'), together with the adjacent nitrogen, canform a heterocyclic ring of five, six or seven members wherein 0 to 1members other than the nitrogen are --O--, --S--, ##STR10## and whichmembers are unsubstituted or substituted by hydroxy, alkyl, aryl,hydroxyalkyl, aminoalkyl, aminoaryl, alkylamino, or carbamoyl whereinthe substituents contain from 1 to about 6 carbon atoms,

p and q can be the same or different and represent integers between 1and 6,

and wherein z of the R^(1') groups are --O⁻ and the remainder of theR^(1') groups are ##STR11##

Also disclosed is a method of performing an NMR diagnostic procedurewhich involves administering to a warm-blooded animal an effectiveamount of one of the above-described complexes and then exposing thewarm-blooded animal to an NMR imaging procedure, thereby imaging atleast a portion of the body of the warm-blooded animal.

DETAILED DESCRIPTION OF THE INVENTION

The complexing agents employed in this invention are derivatives ofwell-known polyaminocarboxylic acid chelating agents, such as DTPA andethylenediamine-tetraacetic acid ("EDTA") and cyclic polyaminocarboxylicacid chelating agents such as 1,4,7,10-tetraazacyclododecaneN,N',N",N"'-tetra acetic acid ("DOTA"). In one class of thesederivatives, free carboxylic acid groups of the chelating agent (thosenot involved in bond formation with the paramagnetic ion) are convertedto aminoalkylamide groups of the formula: ##STR12## For example, if thepolyaminocarboxylic acid chelating agent is DTPA, and the paramagneticion is trivalent, two of the carboxylic acid groups will be derivatizedto the aminoalkylamide form. Likewise, if the paramagnetic ion isdivalent, three of the carboxylic acid groups of DTPA or two of thecarboxylic acid groups of EDTA will be derivatized to theaminoalkylamide form. When these complexing agents are reacted with adivalent or trivalent paramagnetic ion, the resulting complexes aresubstantially non-ionic as evidenced by very low electricalconductivity.

Examples of types of aminoalkylamide derivatives useful as complexesinclude those wherein the aminoalkylamide group is ##STR13## wherein Xis O, S or N, unsubstituted or substituted. In a preferred embodiment,the aminoalkylamide group is a morpholinoalklylamide.

An alternative class of compounds encompassed by this invention,includes cyclic polyamino carboxylic acid chelating agents, such as DOTAand TRITA and represented by the general formula: ##STR14## In theseagents, free carboxylic acid groups are converted to ##STR15## whereinR^(2') is either (CH₂ CH₂ O)_(p) --R^(3') or ##STR16## As with the firstclass of agents described above, if the paramagnetic ion is trivalent,one of the carboxylic acid groups will be derivatized to theaminoalkylamide form, and if the paramagnetic ion is divalent, two ofthe carboxylic acid groups will be derivatized.

Examples of types of derivatives useful as complexes include thosewherein the amino alkylamide group is: ##STR17## In a preferredembodiment, the aminoalkylamide group is morpholinoalkylamide.

The aminoalkylamide derivatives of the chelating agents may be preparedby conventional amide-forming reactions. In general, they are preparedby reacting a stoichiometric amount of an aminoalkylamine with areactive derivative of the polyaminocarboxylic acid chelating agent orcyclic polyaminocarboxylic acid chelating agent under amide-formingconditions. Such reactive derivatives include, for example, anhydrides,mixed anhydrides and acid chlorides. To make complexing agentsrepresented by formula I above, the aminoalkylamine has the generalformula: ##STR18## To make complexing agents represented by formula IIabove, the aminoalkylamide has the general formula: ##STR19##

In one embodiment for making any of these complexing agents, thereactions are conducted in an organic solvent at an elevatedtemperature. Suitable solvents include those in which the reactants aresufficiently soluble and which are substantially unreactive with thereactants and products. Lower aliphatic ketones, ethers, esters,chlorinated hydrocarbons, benzene, toluene, xylene, lower aliphatichydrocarbons, some lower aliphatic alcohols and the like mayadvantageously be used as reaction solvents. Examples of such solventsare isopropanol, acetone, methylethyl ketone, diethylketone, methylacetate, ethyl acetate, chloroform, methylene chloride, dichloroethane,hexane, heptane, octane, decane, and the like. If an acid chloridederivative of the polyaminocarboxylic acid is used as the startingmaterial, then the reaction solvent advantageously is one which does notcontain reactive functional groups, such as hydroxyl groups, as thesesolvents can react with the acid chlorides, thus producing unwantedby-products.

The reaction temperature may vary widely, depending upon the startingmaterials employed, the nature of the reaction solvent and otherreaction conditions. Such reaction temperatures may range, for example,from about 25° C. to about 80° C., preferably from about 25° C. to about50° C.

Following reaction of the reactive polyaminocarboxylic acid derivativewith the aminoalkylamide, any remaining anhydride or acid chloridegroups can be hydrolyzed to the carboxylate groups by adding astoichiometric excess of water to the reaction mixture and heating for ashort time.

The resulting aminoalkylamide compound is recovered from the reactionmixture by conventional procedures. For example, the product may beprecipitated by adding a precipitating solvent to the reaction mixture,and recovered by filtration or centrifugation.

The paramagnetic ion is combined with the aminoalkylamide compound undercomplex-forming conditions. In general, any of the paramagnetic ionsreferred to above can be employed in making the complexes of thisinvention. The complexes can conveniently be prepared by mixing asuitable oxide or salt of the paramagnetic ion with the complexing agentin aqueous solution. To assure complete complex formation, a slightstoichiometric excess of the complexing agent may be used. In addition,an elevated temperature, e.g., ranging from about 20° C. to about 100°C., preferably from about 40° C. to about 80° C., may be employed toinsure complete complex formation. Generally, complete complex formationwill occur within a period from a few minutes to a few hours aftermixing. The complex may be recovered by precipitation using aprecipitating solvent such as acetone, and further purified bycrystallization or chromatography, if desired.

The novel complexes of this invention can be formulated into diagnosticcompositions for enteral or parenteral administration. Thesecompositions contain an effective amount of the paramagnetic ion complexalong with conventional pharmaceutical carriers and excipientsappropriate for the type of administration contemplated. For example,parenteral formulations advantageously contain a sterile aqueoussolution or suspension of from about 0.05 to 1.0M of a paramagnetic ioncomplex according to this invention. Preferred parenteral formulationshave a concentration of paramagnetic ion complex of 0.1M to 0.5M. Suchsolutions also may contain pharmaceutically acceptable buffers and,optionally, electrolytes such as sodium chloride. The compositionsadvantageously can contain one or more physiologically acceptable,non-toxic cations in the form of a gluconate, chloride or other suitableorganic or inorganic salt, including suitable soluble complexes with achelant/ligand, to enhance safety. The chelant/ligand desirably isderived from DTPA or EDTA. Such ligands include the ligands set forthabove used to complex the paramagnetic and or heavy metals to providethe complex formulations of this invention. Advantageously, thecation-ligand complex is provided in amounts ranging from about 0.1 mole% to about 15 mole % of the ligand-metal complex. Such physiologicallyacceptable, non-toxic cations include sodium ions, calcium ions,magnesium ions, copper ions, zinc ions and the like. Calcium ions arepreferred. A typical single dosage formulation for parenteraladministration has the following composition:

    ______________________________________                                        Gadolinium DTPA-di(morpholinoethylamide)                                                                330 mg/ml                                           Calcium DTPA-tri(morpholinoethylamide)                                                                  14 mg/ml                                            Distilled Water           q.s. to 1 ml                                        pH                        7.3 ± 0.1                                        ______________________________________                                    

Parenteral compositions can be injected directly or mixed with a largevolume parenteral composition for systemic administration.

Formulations for enteral administration may vary widely, as iswell-known in the art. In general, such formulations are liquids whichinclude an effective amount of the paramagnetic ion complex in aqueoussolution or suspension. Such enteral compositions may optionally includebuffers, surfactants, thixotropic agents, and the like. Compositions fororal administration may also contain flavoring agents and otheringredients for enhancing their organoleptic qualities.

The diagnostic compositions are administered in doses effective toachieve the desired enhancement of the NMR image. Such doses may varywidely, depending upon the particular paramagnetic ion complex employed,the organs or tissues which are the subject of the imaging procedure,the NMR imaging equipment being used, etc. In general, parenteraldosages will range from about 0.01 to about 1.0 mmol of paramagnetic ioncomplex per kg of patient body weight. Preferred parenteral dosagesrange from about 0.05 to about 0.5 mmol of paramagnetic ion complex perkg of patient body weight. Enteral dosages generally range from about0.5 to about 100 mmol, preferably from about 1.0 to about 20 mmol ofparamagnetic ion complex per kg of patient body weight.

The novel NMR image contrasting agents of this invention possess aunique combination of desirable features. The paramagnetic ion complexesexhibit an unexpectedly high solubility in physiological fluids,notwithstanding their substantially non-ionic character. This highsolubility allows the preparation of concentrated solutions, thusminimizing the amount of fluid required to be administered. Thenon-ionic character of the complexes also reduces the osmolality of thediagnostic compositions, thus preventing undesired edema and other sideeffects.

As illustrated by the data presented below, the compositions of thisinvention have very low toxicities, as reflected by their high LD₅₀values. The low toxicity of these complexes is thought to result, inpart, from the high stability constant of the complexes. The aminoalkylmoieties provide additional sites for the formation of coordinationbonds with the paramagnetic metal ion, thus strengthening thecoordination complex. Therefore, the aminoalkyl groups not onlyneutralize the free carboxylic acid groups of the complexing agent, butthey also participate in the formation of the complexes.

The diagnostic compositions of this invention are used in theconventional manner. The compositions may be administered to awarm-blooded animal either systemically or locally to the organ ortissue to be imaged, and the animal then subjected to the NMR imagingprocedure. The compositions have been found to enhance the magneticresonance images obtained by these procedures. In addition to theirutility in magnetic resonance imaging procedures, the complexing agentsof this invention may also be employed for delivery ofradiopharmaceuticals or heavy metals for x-ray contrast into the body.

The invention is further illustrated by the following examples, whichare not intended to be limiting.

Example 1 Preparation of a DTPA-Morpholinoethylamide Gd Complex

A DTPA morpholinoethylamide Gd complex was prepared in two steps asshown below: ##STR20##

The preparation of [N,N"-bis[N-2((4-morpholino)-ethyl)carbamoyl]diethylenetriamine-N,N',N"-triacetic acid specifically was carried outby the following steps:

A mixture of DTPA-dianhydride (36 g) and aminoethyl-morpholine (27 g) inisopropanol (250 mL) was stirred at ambient temperature for 16 hours.The orange solution was filtered through a fine porosity sintered glassfunnel to remove undissolved impurities. The clear filtrate was pouredonto ether (2L) and the mixture stirred vigorously for 1 hour. Thegranular precipitate was collected by filtration, washed with ether(3×1L), and dried. The pale tan solid thus obtained was sufficientlypure for the next step. Yield 60 g (85%). Anal. Calcd. for C₂₆ H₄₇ N₇O₁₀ ×0.3H₂ O: C, 50.13; H, 7.64; N, 15.74. Found: C, 50.46; H, 7.80; N,15.69. The preparation of[N,N"-bis[N-2((4-morpholino)ethyl)-carbamoylmethyl]diethylenetriamine-N,N',N"-triaceto]-gadolinium(III) monohydrate was carried outas follows:

A mixture of the ligand (13.8 g) and gadolinium oxide (3.6 g) indeionized water (70 mL) was heated at 65°-70° C. (water bath) for 4hours and stirred at ambient temperature for 16 hours. The orangesolution was then filtered through a fine porosity sintered glass funnelto remove undissolved impurities. The clear filtrate was then pouredonto acetone (2L) and the mixture stirred vigorously for 30 minutes.Acetone was decanted off and the gummy residue was further treated withacetone (1L). The gum began to solidify and after 4 hours, theprecipitate was collected by filtration, washed well with acetone(3×1L), dried, and recrystallized from methanol/tetrahydrofuran toafford the complex. Yield, 10 g. (59%). Anal. Calcd. for C₂₆ H₄₄ H₇ O₁₀G_(d) ×1 H₂ O: C, 39.54; H, 5.83; N, 12.42; Gd, 19.89. Found: C, 39.51;H, 5.76; N, 12.47; Gd. 19.79.

Example 2 Preparation of 1,17-Bis(N,N-dimethyl)-4,14-dioxo-3,6,9,12,15-pentaaza-6,9,12-tris(carboxyethyl)heptadecane(1)

A stirred suspension of DTPA-dianhydride (7.0 g., 19.6 mmol) inisopropanol (35 mL) was treated with N,N-dimethylethylenediamine (3.8 g,43.1 mmol). The entire mixture was stirred at ambient temperature forabout 18 hours. The reaction mixture was filtered to remove insolubleimpurities. The clear filtrate was poured into anhydrous ether (2L) andthe mixture stirred vigorously for 1 hour. The fine solid was collectedby filtration, washed with ether (3×200 mL), and dried at 50° C. toconstant weight to yield a colorless solid, 9.0 g (82.0%).

Anal. Calcd. for C₂₂ H₄₃ N₇ O₈.0.5H₂ O (MW 542.63); C,48.71%; H,8.12%;N,18.08%. Found: C,48.50%; H,8.4%; N,18.09%.

Example 3 Preparation of {N,N"-Bis[N-2((dimethylamino)ethyl)carbamoylmethyl]-diethylenetriamine-N,N'N"-triaceto}gadolinium(III)

A mixture of the ligand (11.50 g, 0.021 mol) and Gd₂ O₃ (3.62 g., 0.01mol) in deionized water (50 mL) was heated. After the reaction was over,the filtrate was poured into acetone (1L). The solvent was decanted offand the residue was further treated with fresh acetone (1L). Theprecipitate was collected by filtration and it was recrystallized fromtetrahydrofuran/methanol to yield the complex as a colorless solid, 3.8g (30.0%).

Anal. Calcd. for C₂₂ H₄₀ N₇ O₈ Gd.0.5H₂ O (MW 697.87): C,38.21%;H,5.79%; N,14.18%; Gd.22.72%. Found: C,38.54%; H,6.19%; N,13.99%;Gd,21.79%.

Example 4 Preparation of1,17-Bis(4-thiomorpholino)-4,14,dioxo-3.6.9,12,15-pentaaza-6,9,12-tris(carboxymethyl)heptadecane(4)

A stirred suspension of DTPA-dianhydride (7.14 g, 0.02 mol) inisopropanol (50 mL) was treated with freshly distilledaminoethylthiomorpholine (6.3 g, 0.044 mol). The entire mixture wasstirred at ambient temperature for about 16 hours. The reaction mixturewas filtered to remove insoluble impurities. The clear filtrate wastaken to dryness. The gummy residue was purified by flash chromatographyover reverse phase (C-18) column. This material was used as such formetal complexation.

Example 5 Preparation of{N,N"-Bis[N-2((4-thiomorpholino)ethyl)carbamoylmethyl]-diethylenetriamine-N,N',N"-triaceto}gadolinium(III)

A mixture of the ligand (7.0 g, 10.8 mmol) and Gd₂ O₃ (1.86 g, 5.1 mmol)in deionized water (35 mL) was heated at 67°-70° C. for 18 hours. Afterthe reaction was over, the filtrate was poured into acetone (2L) and themixture stirred vigorously for 30 minutes. After 1 hour, acetone wasdecanted off and the gummy residue was further treated with acetone(1L). The precipitate was collected, washed with acetone andrecrystallized twice from acetone/water to give 4.5 g of colorlesssolid.

Anal. Calcd. for C₂₆ H₄₄ N₇ O₈ S₂ Gd×1.5H₂ O: C,37.54; H,5.66; N,11.79;S,7.70; Gd.18.89. Found: C,37.80; H,5.51; N,11.90; S,7.52; Gd,19.92

Example 6 Toxicity determination of DTPA-morpholinoethylamide Gd complex

The acute intravenous toxicity of the compound of Example 1 wasdetermined as follows: ICR mice, at 1 to 4 per dose level, receivedsingle intravenous injections of the test substance via a lateral tailvein at the rate of approximately 1 ml/minute. The test substances wereat concentrations chosen to result in dose volumes of 5 to 75 ml/kg bodyweight. Dosing began at a volume of 10 ml/kg. Dose adjustments up ordown were made to closely bracket the estimated LD₅₀ with 4 animals pergroup (2 males and 2 females). Observations of the mice were recorded attimes 0, 0.5, 1, 2, 4 and 24 hours and once daily thereafter for up to 7days post injection. On the 7th day post injection, the mice wereeuthanized, weighed and necropsied. Abnormal tissues were noted. At thistime a decision was made as to whether any histopathology was to beperformed and whether or not the tissues should be retained. Necropsieswere also performed on mice expiring after 24 hours post-injection,except for dead mice found on the weekends. The LD₅₀ values, along with95% CI were calculated using a modified Behrens-Reed-Meunch method. Theresults for the complex of Example 1 are reported below:

LD₅₀ : 10.0 mmol/kg (no excess ligand, 0.5M solution)

LD₅₀ : 17.3 mmol/1 kg (5% excess ligand as calcium salt, 0.5M solution)

Example 7 T₁ -Relativity Determinations

T₁ or longitudinal relaxation times were measured at 90 MHz for thecomplex in 25% D₂ O/75%H₂ O mixture at 20 mM down to 0.65 mM. The T₁ isobtained using the spin-echo sequence on the JEOL FX90Q FT-NMRspectrometer. The relaxivities were determined by applying linearleast-squares fit to the 1/T₁ versus concentration data. The targetcorrelation coefficient (r²) is about 0.9990.

All ¹³ C NMR spectra were taken on a JEOL FX9OQQ FT-NMR Spectrometer andall ¹ H NMR Spectra were taken on a Varian Gemini 300 FT-NMRSpectrometer at room temperature. The IR spectrum was done on aPerkin-Elmer IR Spectrophotometer 727. Elemental analyses were performedby Galbraith Laboratories of Knoxville, Tenn., and Atlantic Microlab ofNorcros, Ga. pH measurements were made on a Corning Ion Analyzer 250meter using a Corning combination electrode. All spectrophotometricmeasurements were made on a Varian CARY 2215 uv/vis spectrophotometer atroom temperature. All computer calculations were done on an IBM PersonalSystem 2 or an IBM-compatible PC Kaypro.

The relaxation rate for the complex of Example 1 was 5.13±0.07 mM⁻¹sec⁻¹ at 90 MHz and 25° C. The correlation coefficient (r²) was 0.9993.

Example 8 Preparation of 1-[N-(2-methoxy)ethyl-N-methyl]carbamoylmethyl-4,7,10-tris(carboxymethyl)-1,4,7,10-tetrazacyclododecane

The title ligand is synthesized from DOTA and CH₃ OCH₂ CH₂ NHCH₃ byfollowing the general method reported by Krejearek and Tucker (Biochem.Biophys, Res. Commun. 77 581 (1977)).

Example 9 Preparation of Gadolinium (III)1-[N-(2-methoxy)ethyl-N-methyl]carbamoylmethyl-4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane

A mixture of the ligand from Example 8 (10 gr. 0.021 mol. and Gd₂ O₃(3.6 gr, 0.01 mol) in deionized water (50 ml) is heated at 100° C. untilmost of the solid is dissolved. The mixture is cooled and filteredthrough a 0.2 micron filter to remove insolubles present. The filtrateis passed through an ion exchange column and the fractions containingthe product are concentrated. The product may be further purified, ifnecessary, in accordance with conventional procedures. The procedureproduces the title compound in good yield.

Example 10 Preparation of 1-[N-2-(4-morpholino)ethyl]carbamolymethyl4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane

The title ligand is synthesized from DOTA and 4-(2-aminoethyl)morpholineby following the method reported by Krejearek and Tucker (Biochem.Biophys. Res. Commun. 77 581 (1977).

Example 11 Preparation of Gadolinium (III) 1(-[N-2-(morpholino)ethylcarbamoylmethyl 4,7,10-tris(carboxymethyl)-1,4,7,10-tetrazacyclododecane

The procedure of Example 9 is repeated in all essential details exceptthat the ligand used here is the mono 4-morpholinoethylamide of DOTA,synthesized in Example 10. The procedure produces the title compound ingood yield.

We claim:
 1. A complex having the following formula: ##STR21## whereinM^(+z) is a paramagnetic ion of an element with an atomic number of21-29, 42-44 or 58-70, and a valence Z of +2 or +3,r and s are integersbetween 1 and 6 and can be the same or different, the R' groups can bethe same or different and are selected from the group consisting ofhydrogen, alkyl having from 1 to 6 carbon atoms and mono orpolyhydroxyalkyl, the alkyl portion having from 1 to 6 carbon atoms, theR^(1') groups can be the same or different and wherein at least oneR^(1') is an aminoalkylamide, R^(1') selected from the group consistingof --O⁻ and ##STR22## wherein R^(2') is selected from the groupconsisting of (CH₂ CH₂ O)_(p) --R^(3') and ##STR23## and R^(4') isselected from the group consisting of H, R^(2') and R^(3'), whereinR^(3'), R^(5') and R^(6') can be the same or different and are selectedfrom the group consisting of hydrogen, alkyl, hydroxy, alkoxy, mono- orpoly-hydroxyalkyl, alkoxyalkyl, aminoalkyl or acylamino-alkyl, whereinthe carbon-containing portions contain from 1 to about 6 carbon atoms orR^(5') and R^(6') can, together with the adjacent nitrogen, form aheterocyclic ring of five, six or seven members wherein 0 to 1 membersother than the nitrogen are --O--, --S--, ##STR24## and which membersare unsubstituted or substituted by hydroxy, alkyl, aryl, hydroxyalkyl,aminoalkyl, aminoaryl, alkylamino, or carbamoyl wherein the substituentscontain from 1 to about 6 carbon atoms, p and q can be the same ordifferent and represent integers between 1 and 6, and wherein z of theR^(1') groups are --O⁻ and the remainder of the R¹ groups are ##STR25##2. The complex of claim 1, wherein R^(2') is (CH₂ CH₂ O)_(p) --R^(3').3. The complex of claim 1, wherein R^(2') is ##STR26##
 4. The complex ofclaim 2 or 3, wherein each R' group is hydrogen or alkyl having from 1to 6 carbon atoms.
 5. The complex of claim 3, wherein M^(+z) is chromium(III), manganese (II), manganese (III), cobalt (II), nickel (II), copper(II), praseodymium (III), neodymium (III), samarium (III), ytterbium(III), gadolinium (III), terbium (III), dysprosium (III), holmium (III),or erbium (III).
 6. The complex of claim 4, wherein M^(+z) is gadolinium(III), terbium (III), dysprosium (III), holmium (III) or erbium (III).7. The complex of claim 3, wherein R' is hydrogen, R^(2') is ##STR27##is hydrogen and r and s are each
 1. 8. The complex of claim 3, whereinR' is hydrogen, R^(2') is (CH₂ CH₂ O)_(p) --CH₃, R^(4') is hydrogen oralkyl having from 1 to 6 carbon atoms and r and s are each
 1. 9. Adiagnostic composition suitable for enteral or parenteral administrationto a warm-blooded animal which comprises an NMR imaging-effective amountof a complex of a paragnetic ion having the following formula: ##STR28##wherein M^(+z) is a paramagnetic ion of an element with an atomic numberof 21-29, 42-44 or 58-70, and a valence Z of +2 or +3,r and s areintegers between 1 and 6 and can be the same or different, the R' groupscan be the same or different and are selected from the group consistingof hydrogen, alkyl having from 1 to 6 carbon atoms and mono orpolyhydroxyalkyl, the alkyl portion having from 1 to 6 carbon atoms, theR^(1') groups can be the same or different and wherein at least oneR^(1') is an aminoalkylamide, R^(1') selected from the group consistingof --O⁻ and ##STR29## wherein R^(2') is selected from the groupconsisting of (CH₂ CH₂ O)_(p) -- R³ and ##STR30## and R^(4') is selectedfrom the group consisting of H, R^(2') and R^(3'), wherein R^(3'),R^(5') and R^(6') can be the same or different and are selected from thegroup consisting of hydrogen, alkyl, hydroxy, alkoxy, mono- orpoly-hydroxyalkyl, alkoxyalkyl, aminoalkyl or acylamino-alkyl, whereinthe carbon-containing portions contain from 1 to about 6 carbon atoms orR^(5') and R^(6'), together with the adjacent nitrogen, can form aheterocyclic ring of five, six or seven members wherein 0 to 1 membersother than the nitrogen are ##STR31## and which members areunsubstituted or substituted by hydroxy, alkyl, aryl, hydroxyalkyl,aminoalkyl, aminoaryl, alkylamino, or carbamoyl wherein the substituentscontain from 1 to about 6 carbon atoms, p and q can be the same ordifferent and represent integers between 1 and 6, and wherein z of theR^(1') groups are --O⁻ and the remainder of the R^(1') groups are##STR32## and a pharmaceutically acceptable carrier.
 10. The compositionof claim 9, wherein R^(2') is (CH₂ CH₂ O)_(p) --R^(3').
 11. Thecomposition of claim 10, wherein R^(2') is ##STR33##
 12. The compositionof claim 10 or 11, wherein each R' group is hydrogen or alkyl havingfrom 1 to 6 carbon atoms.
 13. The composition of claim 9, wherein M^(+z)is chromium (III), manganese (II), manganese (III), cobalt (II), nickel(II), copper (II), praseodymium (III), neodymium (III), samarium (III),ytterbium (III), gadolinium (III), terbium (III), dysprosium (III),holmium (III), or erbium (III).
 14. The composition of claim 13, whereinM^(+z) is gadolinium (III), terbium (III), dysprosium (III), holmium(III) or erbium (III).
 15. The composition of claim 9, wherein R^(2') is##STR34## R' is hydrogen, R^(4') is hydrogen, r and s are each 1 andM^(+z) is gadolinium (III).
 16. The composition of claim 10, whereinR^(2') is CH₂ CH₂ OCH₃, R' is hydrogen, R^(4') is methyl, r and s areeach 1 and M^(+z) is gadolinium (III).
 17. The composition of claim 9,which further contains a pharmaceutically acceptable buffer.
 18. Thecomposition of claim 17, which further contains a pharmaceuticallyacceptable electrolyte.
 19. The composition of claim 9, which furthercomprises a complexing agent of the formula ##STR35## wherein R' andR^(1') are as defined as in claim 9 and said complexing agent iscomplexed with one or more physiologically acceptable, non-toxiccations.
 20. The composition of claim 19, wherein said complexing agentis employed in an amount ranging from about 0.1 to about 15 mole % ofthe paramagnetic ion-containing complex and is complexed with one ormore cations selected from the group consisting of sodium ions, calciumions, magnesium ions, copper ions, zinc ions and mixtures thereof. 21.The composition of claim 20, wherein said complexing agent is complexedwith calcium ions.
 22. A method of performing an NMR diagnosticprocedure, which comprises administering to a warm-blooded animal aneffective amount of a complex of the formula: ##STR36## wherein M^(+z)is a paramagnetic ion of an element with an atomic number of 21-29,42-44 or 58-70, and a valence Z of +2 or +3,r and s are integers between1 and 6 and can be the same or different, the R' groups can be the sameor different and are selected from the group consisting of hydrogen,alkyl having from 1 to 6 carbon atoms and mono or polyhydroxylalkyl, thealkyl portion having from 1 to 6 carbon atoms, the R^(1') groups can bethe same or different and wherein at least one R^(1') is anaminoalkylamide, R^(1') selected from the group consisting of --O⁻ and##STR37## wherein R² is selected from the group consisting of (CH₂ CH₂O)_(p) -- R^(3') and ##STR38## and R^(4') is selected from the groupconsisting of H, R^(2') and R^(3'), wherein R^(3'), R^(5') and R^(6')can be the same or different and are selected from the group consistingof hydrogen, alkyl, hydroxy, alkoxy, mono- or poly-hydroxyalkyl,alkoxyalkyl, aminoalkyl or acylamino-alkyl, wherein thecarbon-containing portions contain from 1 to about 6 carbon atoms orR^(5') and R^(6') can, together with the adjacent nitrogen, form aheterocyclic ring of five, six or seven members wherein 0 to 1 membersother than the nitrogen are ##STR39## and which members areunsubstituted or substituted by hydroxy, alkyl, aryl, hydroxyalkyl,aminoalkyl, aminoaryl, alkylamino, or carbamoyl wherein the substituentscontain from 1 to about 6 carbon atoms, p and q can be the same ordifferent and represent integers between 1 and 6, and wherein z of theR^(1') groups are --O⁻ and the remainder of the R^(1') groups are##STR40## and then exposing the animal to an NMR procedure, therebyimaging at least a portion of the body of the warm-blooded animal. 23.The method of claim 22, wherein R^(2') is (CH₂ CH₂ O)_(p) --R^(3'). 24.The method of claim 22, wherein R^(2') is ##STR41##
 25. The method ofclaim 22, wherein M^(+z) is chromium (III), manganese (II), manganese(III), cobalt (II), nickel (II), copper (II), praseodymium (III),neodymium (III), samarium (III), ytterbium (III), gadolinium (III),terbium (III), dysprosium (III), holmium (III), or erbium (III).
 26. Thecomplex of claim 25, wherein M^(+z) is gadolinium (III), terbium (III),dysprosium (III), holmium (III) or erbium (III).
 27. The method of claim22, wherein the pharmaceutically acceptable carrier contains apharmaceutically acceptable buffer.
 28. The method of claim 27, whereinthe pharmaceutically acceptable carrier contains a pharmaceuticallyacceptable electrolyte.
 29. The method of claim 22, wherein thepharmaceutically acceptable carrier contains a complexing agent of theformula ##STR42## wherein R' and R^(1') are as defined as in claim 22and said complexing agent is complexed with one or more physiologicallyacceptable, non-toxic cations.
 30. The method of claim 29, wherein saidcomplexing agent is employed in an amount ranging from about 0.1 toabout 15 mole % of the paramagnetic ion-containing complex and iscomplexed with one or more cations selected from the group consisting ofsodium ions, calcium ions, magnesium ions, copper ions and zinc ions andmixtures thereof.
 31. The method of claim 30, wherein said complexingagent is complexed with calcium ions.